Marker residue, function

The objective of the Residue File is to allow the elaboration of MRLs taking into account the ADI calculated in the Safety File in conjunction with the pharmacokinetics, residues depletion data, and a knowledge of target tissues and marker residues. The individual MRLs in different tissues should be a function of the amount of the food items consumed, and should also reflect the kinetics of the depletion of the residues to be consistent with the established withdrawal periods. MRLs should be proposed in such a way that the total amount of residues ingested with 500 g meat or 500 g poultry or 300 g fish, plus 1500 g milk, plus 100 g egg, plus 20 g honey does not exceed the ADI. The EU uses the daily intake values presented in Table 11.5. After an MRL has been established for a... 

Na and Nb are the numbers of atoms in the two groups A and B and S is the switching function. With the group-based switching function, it is necessary to define the distance between the two groups (i.e. the two points Ta and Tb). There is no definitive way to do this. As with cutoffs, a special marker atom can be nominated within each residue, or the centre of mass, centre of geometry or centre of charge may be used. 

In bone, three proteins have been described which are vitamin K-dependent, osteocalcin (bone Gla protein), matrix Gla protein (MGP), and protein S. Osteocalcin is synthetized by osteoclasts, regulated by the active form of vitamin D, calcitriol. Its capacity to bind calcium needs a vitamin K-dependent y-carboxylation of three glutamic acid residues. The calcium binding capacity of osteocalcin indicates a possible role in bone mineralization, but its exact function is still unclear. However, it is widely used as a serum marker for bone mineralization. Protein S, mainly a coagulant, is also vitamin-K dependent and synthesized in the liver. Children with... 

The first indication that modification of specific tail residues were linked to chromatin functional states, came from immunostaining of Drosophila polytene chromosomes with antibodies specific for H4 acetylated at defined lysines [13]. As shown in Fig. 2A, H4 acetylated at lysine 16 (H4acK16) was found almost exclusively on the transcriptional hyperactive male X chromosome (Fig. 2). (Genes on the Drosophila male X are transcribed twice as fast as their female counterparts so as to equalize levels of X-linked gene products between XY males and XX females.) In addition, H4 lysine 12 was found to remain acetylated in centric heterochromatin, while lysines 5, 8, and 16 were all under-acetylated [13]. These observations led to the suggestion that the histone N-terminal tails constitute nucleosome surface markers that can be recognized by non-histone proteins in a modification-dependent manner to alter the functional state of chromatin [13]. 

Certain residues with a variable degree of conservation can be investigated for their usefulness as evolutionary markers that can provide insight into the history of each enzyme family or clan and allow comparative analysis with other families or clans. Krem and Di Cera [75] identified several such markers with proven evolutionary usefulness. In addition to the use of these markers for rooting the phylogenetic trees, attempts were made to classify serine proteases into functional groups based on these markers or their coding sequences. 

Production of marker fragment-ions is a function of ion velocity in the region before the first mass-resolving quadrupole (5 - 8). Some of the kinetic energy of the ions (a product of their mass and velocity) is converted to internal molecular vibrations upon collision with residual gas molecules in this region. Ion velocity... 

Lactoglobulin (/3-LG) is a very abundant protein found in the milk of mammals (McKenzie, 1971 Liberatori, 1977). The protein has been studied for decades and is considered one of the classical markers for milk proteins. It has been shown by a number of investigators that bovine /3-LG can form a complex with retinol. However, the exact in vivo function of the protein is still not known. The monomer of bovine /3-LG has a molecular weight of 18,000, corresponding to a chain of 162 amino acid residues. There are two genetic variants, commonly known as /3-LG A and )8-LG B (Braunitzer et al., 1973). The differences between the two variants are located at two positions where an Asp and a Val in variant A are substituted by a Gly and by an Ala in form B (McKenzie et al., 1972). Crystal forms of /3-LG A, /3-LG B, and /3-LG A-retinol complex have been obtained. The structures have been determined for the apo structure at 2.5 A (Papiz et al., 1986) and for a retinol complex (Monaco et al., 1987). 

The GFP from the jellyfish Aequorea victoria, although not an enzyme, has become widely used as a marker for gene expression and localization. Although the fluorophore of GFP is not technically a protein-derived cofactor, it is a protein-derived fluorophore. This is another example of posttranslational modifications, which endow amino acid residues with a new function. In this case, the new function is not one which assists in catalysis. Instead, the results of these posttranslational modifications create new fluorescent properties, which serve a different biological function. As with most of the protein-derived cofactors discussed earlier, the presence and identity of the fluorophore is not evident from the amino acid sequence of the protein. The structure of the GFP fluorophore and mechanism of its biosynthesis were deduced from structural analyses. The X-ray crystal structure of GFP revealed that the covalently bound fluorescent chromophore is derived from three adjacent amino acids, serine-tyrosine-glycine on the polypeptide chain (Figure 13). ... 

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